1. Field of the Invention
The present invention relates to a recording head and a recording apparatus using the same, more specifically to an electrical connection in a recording head between a recording element unit formed with a recording element and a drive element unit formed with a drive element for driving the recording element.
2. Description of the Related Art
As a recording element unit and a drive element unit forming a recording head used in a recording apparatus, those which are shown in FIG. 1A and FIG. 1B are known as examples. In FIG. 1A and FIG. 1B, a recording element unit 161 and a drive element unit 162 form a recording head of an ink-jet type, which are formed on a common base plate 1601. Specifically, the recording element unit 161 is composed of a heater 1607, a segment electrical wiring 1608, a common wiring electrode 1613, a common electrode wiring 1614, and the like, which are disposed on a substrate 1604 made of silicon (Si). On the other hand, the drive element unit 162 is composed of a drive element integrated circuit 1606 comprising transistors and the like, electrode wirings 1617 and 1618, and the like, which are disposed on a similar substrate 1605 to the substrate 1604. The respective substrates 1604 and 1605 are connected to the common base plate 1601 with an adhesive or the like. The recording element unit 161 and the drive element 162 are electrically connected one another by a bonding wire 1616.
Details of the recording element unit 161 are shown in FIG. 2. FIG. 2 is a vertical sectional view of the recording element unit shown in FIG. 1A. The heater 1607 for generating heat energy used for ejecting ink from an ejection port of the recording head is formed by connecting the segment electrode wiring 1608 and the common electrode wiring 1614 to a heat generation resistor layer 1620, and on a top layer thereof are formed an ink resistant layer 1654, a cavitation resistant layer, and the like, thereby generating a bubble in the ink utilizing the heat energy generated by the heater 1607, and the ink can be ejected by a pressure of the bubble.
As shown in FIG. 1A, FIG. 1B and FIG. 2, by providing a plurality of heat generation elements in the recording element unit 161, it is possible to obtain an ink-jet recording apparatus that can simultaneously make recording of a plurality of dots using the plurality of the heat generation elements, thereby achieving high-speed recording. In particular, nowadays with increasing requirement for high-density, high-speed recording, simultaneous recording of a plurality of dots in line arranged on a recording medium in a primary scanning direction is generally used. A recording unit is therefore developed in which a large number of heat generation elements (heaters) are disposed in a high density.
Meanwhile, in case that a plurality of heat generation elements are disposed in the recording element unit to make simultaneous recording of a plurality of dots, each heat generation element should be separately ON/OFF controlled. As means for making such a control, a drive element composed of transistors and the like is used as shown in FIG. 1A, FIG. 1B and FIG. 2. This drive element can be formed in the recording element unit, generally, it is independently formed on the respective substrates and then connected to the recording element unit as shown in FIG. 1A, FIG. 1B and FIG. 2. This is because, when the recording element and the drive element are integrally formed on a same substrate, the entire substrate per se will malfunction even when a malfunction occurs in any part of the recording element and the drive element and, in particular, when making a replacement of any elements, the above integrated substrate is required to be replaced.
In case that a recording element board formed with the recording unit and a drive element board formed with the drive unit are separately provided, as techniques for electrically connecting between the boards, there have been known a wire bonding method as shown in FIG. 1A, FIG. 1B and FIG. 2, and a method which uses an electrical connection member 1630 for electrical connection of the substrates 1604 and 1605 with each other as shown in FIG. 3.
In the wire bonding method, to prevent adjacent fine electrodes from contacts each other, a pitch for connecting between respective elements on the recording element board or the drive element board is however required to have some interval. The maximum number of connection parts is necessarily determined when the sizes of the recording element board and the drive element board are determined. In the wire bonding method, since the pitch size is normally as large as about 0.2 mm, the number of connection parts is required to be reduced. On the contrary, when the number of connection parts in the recording element board or the drive element board is previously determined, this means that the sizes of the recording element board and the drive element board have to be very long.
In the method of using an electrical connection member as shown in FIG. 3, there are requirements for size reduction and cost reduction.
As one which solves such problems, a construction for electrical connection as shown in FIG. 4 is proposed. That is, electrical connection is achieved by bump-shaped electrodes 1630a and 1630b which are protrudingly provided at an end of an electrode wiring. Compared with the above described wire bonding method and the method of using the electrical connection member, this method has advantages that high density wiring is extremely easy, compact construction and cost reduction are easy, and the like.
A construction of recording head using this method comprises a recording element having a wiring for supplying an electrical signal to the heater and a holder for holding the wiring, and a bump-shaped electrode protrudingly provided at an end of the wiring. A liquid passage communicating with an ejection port for ejecting the ink is provided in accordance with the heater as an energy generator of the recording element.
Another construction comprises a recording element unit including a recording element having a wiring for supplying an electrical signal to the heater and a holder for holding the wiring, and a bump-shaped electrode protrudingly provided at an end of the wiring, and a drive element unit having a drive element for driving the recording element and a wiring connected to the drive element, wherein the bump-shaped electrode and the wiring of the electrical drive element board are connected, and a liquid passage communicating with an ejection port for ejecting the ink is provided in accordance with the heater as an energy generator of the recording element.
In the above construction, a patterned wiring and the bump-shaped electrode are as follows: The patterned wirings of the recording element and drive element boards are formed on the surface of the holder. Further, when a protective layer for protection and insulation of the patterned wiring is formed on the surface of the holder, it is necessary to expose a sufficient area to form the bump-shaped electrode. The patterned wirings are formed of a conductive material such as Al or the like. A connection part comprising a bump-shaped electrode is formed on the patterned wiring of the recording element board.
The connection part comprising the bump-shaped electrode is for making electrical connection with another circuit boards. That is, "electrical connection" is achieved by directly bonding with connection part of other circuit boards and the like. Material of the bump-shaped electrode can be such metals as Cu, Ni, Au, Cr, Rh, or alloys thereof. The bump-shaped electrode and the patterned wiring may be integrally formed from the beginning of production, or after the patterned wiring is formed, the bump-shaped electrode may be formed on the patterned wiring.
Utilizing the above bump-shaped electrode, "bonding" is carried out as shown in FIG. 4. In this case, "bonding" provides particularly advantageous effects when the connection part of the recording element board and the connection part of the drive element board are bonded by a pressure bonding method. "Connection" may be "bonding" by metals or alloys, or may be "bonding" by a method by other than metals and alloys, and may be a combination of these methods with a pressure bonding method.
In this method, as already disclosed, it is important that positional deviations of tips of the bump-shaped electrodes due to surface curves or irregularities of the recording element board and the drive element board are absorbed to assure reliability of electrical connection between the recording element board and the drive element board.
However, in general, an electrical circuit board is not a perfectly flat plate but has some curves or irregularities, or due to heat evolution during driving, deflections may be generated. When there are large curves or irregularities as above, a connection failure may be generated in electrical connection of the recording element board with the drive element board.
To avoid this, it is preferable to strengthen the connections or use a substrate having no curves or irregularities. However, this method has a problem of a substantial increase in cost. Further, the above effect of curves will be increased as the heater arrangement direction of the recording element unit becomes longer. To solve such a problem, it is proposed to form a bump-shaped electrode through a layer of large thickness. With this method, a relatively good bonding can be made.
However, there are problems that cannot be satisfactorily solved even by the above-described methods. That is, in a construction in which a plurality of bump-shaped electrodes are arranged on a substrate and press bonded to obtain electrical connection, compared with reliability of the first press bonding, the reliability becomes deteriorated while repeating press bonding, and a connection failure may occur after some repetitions.
It has been elucidated by investigations thereafter that when the above bump-shaped electrodes are bonded with each other, since reliability of press bonding is increased by plastic deformation of these bump--shaped electrodes in a direction along its transverse sectional plane, when press bonding is repeated for replacement or the like of one board, reliability of connection may be deteriorated due to deformation of the bump-shaped electrodes.
On the other hand, in the already described recording element unit and the recording apparatus using the same, durability of the recording element unit is generally shorter than the service life of the recording apparatus.
Therefore, in a recording apparatus, when a malfunction occurs in the recording element unit, it is desirable to replace the recording element unit, the malfunctioned recording element unit must be replaced as simply as possible, and, after replacement, assured to have the same reliability as before replacement.
Further, it is general that the recording element board is shorter in service life compared with the drive element board. This is because a plurality of recording elements disposed in the recording element unit are substantially shorter in service life than drive elements of the drive element unit.
Under such circumstances, in the above-described recording apparatus, the recording unit, in particular its recording element board is frequently replaced. Further, when replacing the recording element board, the drive element board is naturally not required to be replaced. Further, from the cost point of view, the drive element board is a module comprising semiconductor devices and is thus high in cost, the drive element board is required to be used, as is, without replacement, even when the recording element board is replaced.
However, as already described, it has been found that in the connection arrangement using the bump-shaped electrodes, reliability of bonding is deteriorated during repeated press bonding, and unbonded devices are generated.
FIGS. 5A to 5E are schematic side views showing this condition, respectively.
As shown in FIGS. 5A and 5B, when the recording element board 1604 and the drive element board 1605 are connected with each other, the bump-shaped electrodes 1630a and 1630b are press bonded with one another. In this case, if there are errors in height or positional deviations or irregularities on the substrate in three bump-shaped electrodes 1630b of the recording element board 1604, the bump-shaped electrode 1630a of the drive element board is irregularly deformed by height errors and the like of the bump-shaped electrodes 1630b of the recording element board. When the recording element board 1604 is removed for replacement (FIG. 5C), and a new different board 1604 is mounted (FIG. 5B), an unbonded bump-shaped electrode may be generated because of the above irregular deformation generated by press bonding with the former board 1604 (FIG. 5E).
With a view to eliminate the above problems, an object of the present invention is to provide a recording head which can prevent deterioration of reliability of press bonding of a bump-shaped electrode due to repeated bonding between circuit boards and a recording apparatus using the same.